In　order　to　get　the　influence　rule　of　the　cumulative　damage　caused　by　the　horizontal　bilateral　load　coupling　effect　on　the　hysteretic　behavior,　strength　and　stiffness　degradation　of　the　reinforced　concrete　(RC)　box　pier,　the　biaxial　restoring　force　model　of　the　RC　box　pier　was　investigated.　Firstly,　the　biaxial　pseudo　static　test　and　finite　element　simulation　of　the　RC　box　pier,　considering　axial　load　ratio,　slenderness　ratio,　reinforcement　ratio　and　loading　angle,　were　conducted,　and　the　calculation　formula　of　the　damage　factor　considering　the　bidirectional　coupling　load　effect　was　also　presented.　Secondly,　the　skeleton　curves　of　the　testing　piers　were　idealized　as　a　three-line　type　model　with　the　descending　segment,　and　the　calculation　method　of　the　skeleton　curve　and　the　corresponding　stiffness　for　the　RC　box　pier　were　established.　Finally,　the　relation　between　the　damage　factor　and　the　strength　and　stiffness　degradation　of　the　specimens　were　analyzed　according　to　the　characteristics　of　the　experimental　hysteretic　curves,　whilst　the　calculation　formula　of　the　load-steep-descending　factor　from　the　unloading　point　of　the　peak　displacement　was　proposed.　At　the　same　time,　the　biaxial　hysteresis　rules　of　the　box　pier　was　given,　and　the　damage-based　biaxial　restoring　force　model　for　the　RC　box　pier　was　established.　The　results　show　that　the　calculating　skeleton　and　hysteresis　curves　from　the　proposed　restoring　force　model　of　the　RC　box　piers　agree　well　with　results　of　the　quasi-static　testing,　and　the　maximum　error　is　less　than　10%.　The　proposed　model　reflects　the　damage　aggravated　effects　and　hysteresis　characteristics　caused　by　horizontal　bi-directional　loading,　so　it　will　provide　the　theoretical　reference　for　the　multi-dimensional　seismic　analysis　and　design　for　the　RC　box　pier.　©　2017,　Editorial　Department　of　China　Journal　of　Highway　and　Transport.　All　right　reserved.